The fourth dimension in crime mapping at the RATP
tel : 01 48 15 28 62
tel : 01 43 03 98 44
Central IV - 1, avenue Montaigne
F - 93160 Noisy le Grand
The RATP manages the urban transport network of Paris and its suburbs. It has to ensure the safety on this network. The service in charge of the security registers delinquent acts specifying place and time, and draw maps in an automatic way. The produced maps are thematic inventory maps corresponding to a determined moment or period. Each map lets have a good punctual apprehension of the phenomenon, but their accumulation in large number makes difficult the perception of its evolutivity in the time. Security, however, intends to be able to make previsions, and the search for repetitive or cyclic spatio-temporal behaviors is therefore primordial.
The "typical" map produced by the security service contains only nodes (subway and Rapid Transit System stations and bus stops) of the network to which is applied the number of delinquent acts for a " time step ".
If maps for successive time steps gathered in a collection of maps give a global vision of the phenomenon, it does not translate its dynamics. How, indeed, could we perceive in a continuous way the transition between a state and the following one? How, to the three dimensions of the map (X, Y and Z), can we add the fourth dimension, TIME ?
This question is illustrated by the scheme below, inspired by the principle of cartoon:
To obtain the expected effect, several solutions have been considered (Animated GIF, Flash, Morphing) and left for the SVG solution. The properties of SVG : XML compatibility, Style sheet (CSS), Cartesian coordinates, interactivity, animation (SMIL) squares the specifications (automatic production, fluidity…)
Computing allowed to create an application producing automatically an animation of maps in a SVG file integrated into a HTML page, using Oracle data extracted by an Access request, going through ArcView.
Different time steps have been tested from the twenty-four hours a day to the twelve months a year, through the seven days a week and the thirty days a month.
These "movies", reveal various evolutions of crime within the transport network, replying or not to actions of security teams:
- transfers of crime to other stations (delinquents move together to another station)
- distribution in the neighboring stations (delinquents scatter into the other stations)
- parallel evolution (delinquents act at the same time in several stations).
If some of these behaviors were already known, many have been revealed by cartographic animation.
The Security Service feels the crime’s pulse very easily (without any heavy statistical computing), and the security teams can be sent to the right place at the right moment for better safety of the travelers.